1. Field of the Invention
The present invention refers to an endoprosthesis for a knee joint. More particularly, it relates to an endoprosthesis including a portion which is adjustable in length after implanting.
2. Description of the Prior Art
For patients who are still growing and who receive a total endoprosthesis for the knee joint, for example, an adaptation to the growth in length of their bones is necessary. U.S. Pat. No. 4,892,546 discloses a so-called growth prosthesis comprising a pair of telescopically co-acting rod members defining a bone replacement part, wherein a spindle and a spindle nut provide for a relative adjustment of the rod members. The spindle of the known prosthesis is coupled to a bevel gear of which a gear wheel includes a drive pin which may be actuated from outside the prosthesis. Preferably the drive pin is located in an area of the joint where the thickness of the soft tissue is relatively thin so that the bevel gear becomes accessible by a mere prick incision. Therefore, only local anesthesia is required to adjust the prosthesis in length. Nevertheless an operation, although minor, is necessary. This results in a certain stress and risk to the patient.